fetch broken in SSR on Cloudflare Pages

[Deebster]

Describe the bug

Attempting to fetch from +page.ts fails. The original error I came across said Failed to get the 'credentials' property on 'Request': the property is not implemented.

I posted about this in the Cloudflare Discord and the finger was pointed at https://github.com/sveltejs/kit/pull/5116/files.

In the original issue it was stated "At the time this hack was added, the workers runtime didn't support the credentials header set on a request - this looks to be support now" but the Cloudflare people on the Discord don't agree with this.

I made a minimal test repo, although in this case the error is different: Failed to get the 'mode' property on 'Request': the property is not implemented.

I haven't tested this when publishing via Wrangler, but they share the same runtime so I would expect it to be broken in that case too.

Reproduction

tl;dr: Publish https://github.com/Deebster/sveltekit-broken-fetch on Cloudflare Pages.

Full steps

In Github:

• Fork https://github.com/Deebster/sveltekit-broken-fetch

In Cloudflare:

• Go to Pages
• Create a project > Connect to Git
• Select repo
• In "Build settings":
  • Set "Framework preset" to "SvelteKit"
  • Add Environment variable NODE_VERSION with value 16
• Click "Save and Deploy"

In browser:

• View webpage.

Logs

Error: Failed to get the 'mode' property on 'Request': the property is not implemented.
    at fetch (worker.mjs:1427:24)
    at async fetcher (worker.mjs:1414:22)
    at async load (worker.mjs:603:22)
    at async load_data (worker.mjs:1690:16)
    at async worker.mjs:2496:18

System Info

Cloudflare Pages

Severity

blocking an upgrade

Additional Information

Anyone using current version of SvelteKit cannot do fetch in SSR on Cloudflare Pages.

[Deebster]

My original error had the stack trace

Error: Failed to get the 'credentials' property on 'Request': the property is not implemented.
    at fetch (worker.mjs:1588:81)
    at options.hooks.handleFetch (worker.mjs:3239:77)
    at fetcher (worker.mjs:1581:42)
    at load (worker.mjs:633:24)
    at load_data (worker.mjs:1857:39)
    at async worker.mjs:2663:18

[Conduitry]

The error message you say you're able to reproduce in a minimal repro is the same as #6739. So this should either be closed in favor of that, or we need a separate repro if there really is a different bug going on.

[Deebster]

@Conduitry yes, this does appear to be the same issue as #6739 (Pages/Wrangler aside). I'll see if I can get a repro of my original error - I'd got most of the way through the report before noticing.

[benmccann]

Ok, I'll close this as a duplicate then to help keep track of things and would recommend you file a new issue if you're able to reproduce the other error. Thanks!